Measurement of intra-ocular pressure (IOP) is an important procedure in diagnosing various diseases and abnormalities of the eye as well as monitoring status of ophthalmic therapies and procedures.
IOP is measured by a device called tonometer. Traditional stationary tonometers are used only in an ophthalmologist's office environment and only in a vertical position. There are two basic types of tonometers: the Goldmann-type which has been a universally recognized standard instrument which relies on the direct contact with a subject's cornea, and contact-less tonometers which use a puff of air to achieve flattening or “applanation” of the cornea and then compute the IOP as a function of the air pressure required for such corneal applanation.
Contact tonometers require anesthesia of subject's cornea and carry a potential risk of transmitting eye infection from one subject to another and also a potential damage to the cornea itself if the device is not applied correctly or is improperly calibrated or maintained.
Both of these types of tonometers are quite large and heavy, up to 40 lbs (18 kg) as is in case of the Topcon CT-80 computerized tonometer made by Latham & Philips Ophthalmic Products, Inc. They are therefore consigned to medical offices. They also generally operate only in vertical position and require subjects to be cooperative while a measurement is performed. One non-contact tonometer, Pulsair EasyEye by Keeler, Inc. has a movable measuring head connected to a stationary base, which limits the range of its deployment and utility.
Another type is a contact tonometer which measures IOP by compressing the subject's cornea through the eyelid. One such tonometer made by the Tonopen, Inc. is portable but requires considerable skill for its use to achieve repeatable and reliable readings. The same can be said for the Diaton tonometer marketed by BiCom, Inc. These tonometers require several readings to be taken and then averaged due to the variability of the measurement process.
Measurement of IOP in different subject's positions sometimes results in differing readings, so some medical practitioners suggest measuring it at several different positions.
Uncooperative subjects such as small children have to be sedated in order to perform an IOP measurement. In case of the elderly or in an emergency room setting there's also a need to measure IOP when the subject is prone.
It has been recommended for some cases for the IOP measurements to be performed more or less continuously, as IOP displays diurnal variation which may not be adequately captured and evaluated when a patient has to visit a medical office for an IOP measurement.
It is desirable, therefore to have a means to measure, store and transmit IOP readings remotely, possibly several times a day, without a visit to the doctor's office, while at the same time providing information to the patient.
It is also desirable to have a portable tonometer which can be easily transported and used at subject's home, a tonometer which would be also easy to use both by non-specialist personnel and subjects themselves.
It is also desirable for a tonometer to operate in any position and be usable with pediatric and geriatric patients and other ‘difficult’ subjects, like those encountered in veterinary practice, without anesthesia or constraints.